Internal combustion engines are devices in which reactants (e.g., fuel and an oxidizer) are combusted in a combustion chamber to produce high-pressure gas so as to apply force to another component of the engine. The typical components of an internal combustion engine are well known to those of ordinary skill in the art. These components generally include cylinders, pistons, valves, the cylinder head, the crankshaft, the camshaft, and the engine block.
Combustion of the reactants takes place inside a combustion chamber, which is generally formed by the cylinder heads, cylinders, and the tops of the pistons. In spark ignition engines, a spark is used to ignite the reactants. In compression ignition engines, the heat created by compression ignites the reactants. Regardless of how the reactants are ignited, the resulting combustion produces heat and pressure that act on the moving surfaces of the engine, such as the top of the piston. The pistons are generally attached to a crankshaft via connecting rods, which transfer the motion of the pistons into rotational motion.
Most internal-combustion engines are four-stroke engines. A four-stroke engine is one in which the piston(s) must complete four movements, or strokes, to produce power. This is also known as the “Otto” cycle. Typically, a four-stroke engine works as follows. During the first stroke, intake, the piston descends, drawing the reactants into the combustion chamber through an inlet valve. The piston continues downward until it reaches the point at which it is farthest from the cylinder head, i.e., bottom dead center. At the start of the second stroke, compression, the inlet valve closes, and the piston moves upward to the point where it is closest to the cylinder head, i.e., top dead center. In the third stroke, power, the compressed reactants are ignited, forcing the piston downward. An outlet valve opens and the piston moves back upward to complete the last stroke, exhaust. The four-stroke cycle is then repeated.
A commonly cited problem with the four-stroke engine is that it operates at only one-third efficiency. In other words, only a third of the potential fuel energy is delivered to the crankshaft. Two thirds of the energy is lost either through the exhaust or as waste heat. Thus, due in part to increased fuel-efficiency standards, numerous variations have been introduced to improve engine efficiency. See U.S. Pat. Nos. 8,434,305, 8,347,850, 7,810,459, 6,543,225, 4,776,306, 4,099,489, 3,871,337, 2,988,065, 2,058,705, 1,790,534, and 608,845; WO Pubs. 2005068812, 2004027237; EP Pubs 1,148,219, 1,170,478, 1,312,778, 1,607,594, 1,895,138, 2,088,283; and David Scott, “Paired-Cylinder Engine, ” Popular Science February 1978. Each and every reference cited herein is hereby incorporated by reference in its entirety, where appropriate, for teachings of additional or alternative details, features, and/or technical background.
One alternative to the traditional four-cycle engine is the split-cycle engine, in which the four strokes are shared between two cylinders. In a split-cycle engine, the intake and compression strokes take place in one cylinder. The compressed reactants are then transferred to a second cylinder, in which the power and exhaust strokes are performed. Transference between the first and second cylinder typically occurs via a crossover chamber, which is closed off via a valve before ignition in the second cylinder. Outside of split-cycle engines, communication of the reactants between two cylinders is uncommon in engine design.
The Scott article, cited above, describes a pair of pistons connected by a recess in the block face, where the pistons perform separate “mixture-induction” and “air-swirl” functions. However, this design causes additional cost and efficiency problems. For example, while the cylinder head is easily replaceable, the block face is not. One advantage of the current invention is that it can be created from existing engines efficiently and inexpensively by modifying the cylinder head and the crankshaft or connecting rods.
Traditionally, ignition is timed so that combustion occurs near the end of the compression stroke, i.e., slightly before top dead center. This is needed because the reactants do not completely burn at the moment that the spark fires. Thus, by advancing the spark before top dead center, combustion actually occurs when the combustion chamber reaches its minimum size. Generally, sparks occurring after top dead center are thought to be counter-productive, producing excess waste. Only a few small engines are designed to ignite after top dead center.
Knocking is another engine complication that occurs when the reactants are unintentionally combusted at the incorrect moment. Knocking can cause severe engine damage. In a spark ignition engine, the reactants are meant to be ignited only via the spark plug at the precise time of ignition. Knocking, or abnormal combustion, occurs when a pocket of the reactants are detonated outside the boundary of the flame front. Knocking can be caused by pre-ignition, when the reactants ignite before the spark plug fires.
The prior-art engines discussed herein are to be considered conventional engines where appropriate.